Insurgent was written by Veronica Roth.
After surviving the attack, Tris wants to find out why the Abnegation had to die. What did they want to protect from the Erudite?
Story wise, Divergent was definitely better than Insurgent because there were way more ups and downs in Divergent. But I thought Insurgent was kind of on the same level as Divergent because of the whole struggle Tris went through in this book. That also builds up for the grant finale of Allegiant which I yet have to read.